A liquid crystal display, in general, comprises a pair of spaced, parallel plates, generally of glass, each having an electrode of a conductive material on its surface facing the other plate, and a liquid crystal material between the electrodes. The electrode on one of the plates, generally the back plate, is divided into a plurality of individual, spaced areas which are arranged in a plurality of spaced parallel rows and columns. Each of the areas of the electrode forms a pixel of the display. Between each pair of adjacent columns of the pixel areas is a conductive line which forms a data line and which is electrically connected to each of the pixel areas in an adjacent column. Between each pair of adjacent rows of the pixel areas is a conductive line which forms a select line and which is electrically connected to each of the pixel areas in an adjacent row. Generally, each data line is electrically connected to each pixel area through a MOS transistor, and each select line is electrically connected to each pixel area through a capacitor.
Referring to FIG. 1, there is shown a top plan view of one pixel of a prior art liquid crystal display 10. The liquid crystal display 10 comprises a base plate 12 of an insulating material, such as glass, having on a surface thereof, an area 14 of a conductive material, such as polycrystalline silicon. The area 14 forms a pixel of the liquid crystal display 10. It should be understood that the liquid crystal display 10 includes a plurality of the pixel areas 14 arranged in an array of spaced rows and columns. The pixel area 14 is shown as being substantially in the form of a rectangle. Extending across the top portion of the pixel area 14 is a select line 16 of a conductive material, such as polycrystalline silicon. The select line 16 is insulated from the pixel area 14 by a layer of a dielectric material (not shown), such as silicon oxide, preferably silicon dioxide, or silicon nitride. Extending along one side of the pixel area 14 is a data line 18 of an electrically conductive material, such as a metal.
The data line 18 is electrically connected to the pixel area 14 by a MOS transistor 20. The MOS transistor 20 is formed by a strip 22 of polycrystalline silicon extending from the pixel area 14, across which extends the polycrystalline silicon select line 16' of the next adjacent pixel area 14'. The select line 16' is insulated from the strip 22 by a layer of insulating material (not shown), such as silicon oxide, preferably silicon dioxide. Thus the select line 16' serves as the gate of the MOS transistor 20. The data line 18 is electrically connected to the strip 22 on the side of the select line 16' away from the pixel area 14. Thus, the portions of the strip 22 at opposite sides of the select line 16' serve as the source and drain of the MOS transistor 20.
The portion of the select line 16 which extends across the pixel area 14 and which is spaced from the pixel area 14 by the dielectric material forms a capacitor with the pixel area 14. The capacitor serves to stabilize the pixel voltage in the presence of leakage current and charge noise. To provide improved stabilization, it is desirable to have as large a capacitor as possible. One means for increasing the capacitance is to increase the size of the select line 16 so that it extends over a larger portion of the pixel area 14. However, this would take up a larger portion of the pixel area 14 and thereby decrease the active area of the pixel area 14 and decrease the aperture size of the pixel. If the pixel area 14 is made larger to allow for increased capacitance without decreasing the active area, the overall size of the display would be increased. Therefore, it would be desirable to be able to increase the capacitance of the capacitor between the select line and the pixel area without decreasing the active area and aperture size of the pixel and without increasing the overall size of the display.